An endless belt conveyor system commonly includes the endless conveyor belt, an assembly for driving the belt at the one end of the system and a trailing assembly at the opposite end of the system to support and return the belt to the drive assembly. The drive and trailing assemblies are typically positioned to maintain the belt under the proper operating tension and to provide some, usually limited, lateral guidance to maintain the belt in proper tracking alignment. In some applications, additional intermediate assemblies may also be used to further guide and support the belt.
There are many factors that may adversely affect the operation of the driving and trailing assemblies, particularly in systems using metal belts and helical or spiral weave, woven wire belts. These include the loading requirements of the system, the vertical and horizontal space allowed for the drive and trailing assemblies, the operational temperature of the system, the inclines or side loading areas in the system and the operational conditions of the system (i.e. corrosive conditions, damp conditions, large temperature extremes, loose particles and debris, etc.). The drive and trailing assemblies in such applications must also frequently operate at high speeds for extended periods without adverse effects on the belt tension, belt tracking or belt durability.
In many conveyor systems, the drive and trailing assemblies use a smooth rubber or friction surfaced pulley to engage and propel the belt through the system. These pulleys, however, usually lack the ability to positively engage the endless belt or ensure proper tracking of the belt, and thus are frequently prone to slippage and loss of drive efficiency, particularly when the above factors create a difficult operating environment. Other systems use expensive, and sometimes difficult to maintain, direct drive chain links mounted on the sides of the belt to engage outboard drive sprockets. These systems may reduce belt slippage and increase drive efficiency under extreme operating conditions, but are often not cost effective for the conveyor system manufacturer or the end user.
Relatively expensive and difficult to manufacture toothed sprocket systems have also been used to provide a positive drive for endless belt conveyors. These sprocket systems commonly rely on a limited, single engagement point between the sprocket teeth and the belt. In conveyors subject to substantial temperature ranges and extremes, the differential of thermal expansion between the belt and sprocket frequently interferes with this limited engagement between the toothed sprocket and belt. As a result, such systems may be inefficient, cause mistracking of the belt and fail to provide the belt with sufficient lateral support.
In addition, toothed sprockets are typically operable in only one direction. Thus, it is difficult, if not impossible, to reverse the direction of travel of the endless belt in such systems without rearranging or reworking the sprockets and other major components of the system.
In applications with strict vertical space limitations, as in cooling chambers and other operations using staggered, stacked belts, it is frequently desirable for cost and technical reasons to use woven wire belts with the largest mesh size compatible with the products carried by the belts. When the size of the belt mesh is increased, however, it is usually necessary to increase the diameter of the pulleys used in the system. An estimate used for systems employing drive and trailing pulleys is that the required pulley diameter in inches is equal to 180 divided by the number of mesh openings per linear foot along the length of the belt.
In the case of a belt with 16 mesh openings per linear foot of length, for example, the expected diameter for the pulleys in the system would be at least 11.25 inches. However, the vertical space available for drive and trailing assemblies in staggered, stacked conveyor systems often cannot accommodate pulleys of such sizes. Pulleys with smaller diameters may be used, but this often creates deleterious belt deformations as the belt passes over the pulleys. These deformations may reduce the life of the belt and interfere with the belt alignment, particularly in high speed systems. Consequently, more costly, smaller mesh belts are frequently used in these applications, sometimes at the expense of the operating efficiency of the entire system.
The drive and trailing assemblies, in addition, are often required to maintain the conveyor belt at high tension levels without imposing significant strains on the structural elements of the belt. In some prior art systems, including those using multiple toothed sprockets, the drive and trailing assemblies failed to provide sufficient lateral support to the belt under high belt tension conditions, and in some instances increased the stresses and strains on the belt. In those systems, the belts intermittently dished, stretched, warped or curled during operation of the conveyor system. As a result, the belts were damaged before full scale use of the system commenced, the useful life of the belt and other components of the system were significantly curtailed, and the overall maintenance costs for the system were significantly increased.
The drive and trailing assemblies, furthermore, should be relatively easy to install and maintain. Drive assemblies requiring multiple and complicated components that require extensive start-up efforts and further close attention during operation of the system add substantial, undesirable expense to the overall cost of such systems. Similarly, the drive and trailing assemblies must be cost effective to purchase and include components that are durable and replaceable at a reasonable cost to the original system manufacturer and to the end user.
This invention overcomes the limitations of the prior art to provide an efficient, cost effective conveyor drive system, particularly for systems employing woven wire endless belts. The drive and trailing assemblies (as well as intermediate assemblies) of the invention provide a positive drive for endless belt conveyor systems that supports and maintains the belt in proper tracking alignment, is reversible and prevents undue stress on the belt members during high speed at high tension operations. This invention further provides a drive that is space efficient, suited for different operating conditions, including large temperature extremes and is very flexible in construction and use.